<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        body{
            text-align: center;
        }
        canvas {
            border: 1px solid #000;

        }
    </style>
</head>
<body>
<canvas width="500" height="500" id="cas"></canvas>
</body>
<script>
    var cas=document.getElementById('cas');
    var ctx=cas.getContext('2d');
    ctx.arc(cas.width/2,cas.height/2,100,Math.PI/-3,2/3*Math.PI);
    ctx.stroke();
</script>
</html>